Retinotopic mapping of the visual field onto primary visual cortex (V1) is accompanied by an orderly, fine mapping of ocular dominance and preferred orientation in macaque. Other stimulus dimensions to which cells in V1 are tuned include at least color, direction of motion, spatial frequency and binocular disparity. Electrophysiological studies by the PI and co-workers revealed that in the extrastriate area V4, cells are similarly tuned for orientation, color, direction of motion and spatial frequency. In addition, a silent, suppressive zone surrounded the excitatory center of cells in V4. The silent, suppressive surround, a mechanism present in end-stopped cells of V1 and prominent in V4, may be involved in figure/ground separation and color-constancy. The general goal of this proposal is to determine the functional architecture for visual stimulus dimensions in V1 and V4 in macaque, with attention to the nature of the suppressive surrounds. The electrophysiological studies of the V4 surround mechanism focused on spectral preferences and revealed that cells were most suppressed when the color in the surround was the same as that in the center. The first aim of this proposal is to continue the physiological study of the surround in order to understand the underlying mechanisms of such phenomena as figure/ground separation and color-constancy. Extension of the work is therefore proposed to other stimulus dimensions and to further study of color in V4. The second specific aim of this proposal is to investigate the functional architecture in V1 and V4 for orientation, color, direction of motion and spatial frequency, using activity labeling procedures and confirmation by physiological recordings. Previous work by the PI created methods for fine-resolution 2DG labeling of monkey brain with quantitative retention of label, as well as for double-2DG-labeling to label the activity distributions for two different conditions. Ultimately, the answers should specify whether these stimulus dimensions are mapped in these areas and how the functional architecture represents the information.